Chapter One
Introduction
MAN_905G_1.16
Page 16
As well as the normal “I/O change” messages and update messages, the 905G has “block
read” and “block write” messages for use with other 905G modules. These messages will
transmit multiple register values instead of only one as in the normal 905U message. The
block read/write messages increase the efficiency of radio communications where a 905G
“sees” a large number of changes in its database at the one time. For example, if a host
writes a block of 100 signal values to a 905G, and 20 of these values have changed since the
last write-operation. If the block is mapped to another 905G, then the 905G can transmit all
20 values in one radio message, instead of 20 messages.
Normal I/O messages can be repeated by any type of 905U I/O module, however block
read/write messages can only be repeated by other 905G modules.
Block Read Message
A block read message is a request to another 905G to transmit the values of a consecutive
block of registers. The destination 905G will respond with the values, which will be stored in
a corresponding block of registers in the originating 905G. A block read message can be
triggered by:
♦
time period, configurable 1 – 4096 sec (1.1 hour), or
♦
real time clock, or
♦
on demand by the host device, by writing to a “trigger register” in the 905G.
Block Write Message
A block write message transmits a consecutive block of register values from one 905G to a
destination 905G. It can be triggered by:
♦
time period, configurable 1 – 4096 sec (1.1 hour), or
♦
real time clock, or
♦
on demand by the host device, by writing to a “trigger register” in the 905G, or
♦
a change-of-state event occurring within the block of I/O registers.
If a block write message has been configured to be transmitted on change-of-state, a “time
window” is configured. When a change-of-state occurs in one of the registers in the block,
the time window will be activated. All changes during the time window will be grouped
together and transmitted as one block write message. That is, the block write message will
not be sent immediately the first change-of-state occurs (unless the time window is
configured to zero), but will be sent at the end of the time window - any other registers in
the block that change during the time window will be sent as part of the same message. The
time window can be configured from 0 – 255 seconds.
1.3.3
“Data Concentrator” Networks
905G units can act as “data concentrator” units to collect I/O from a local network of 905U
wireless I/O modules and pass the I/O on to another 905G as a block.
